I also use them but be sure there are no defects in the tub as I had to replace one because they chewed a whole it it because it was bubbled up in the one corner. But this is the rat rack I have just recently built.
Front view minus 2 tubs. I made it to hold eight but lowes only had 6 at the time.

This is a side view with the braces. The rails were a lil crooked but have them fixed now.